1. Field of the Invention
The present invention generally relates to the field of telephone systems, and more specifically, to activity detection mechanisms in telephone systems.
2. Description of the Related Art
Subject to state Public Utility Commission regulations, ownership of Customer Owned Coin Operated Telephone (COCOT) service is permitted. An outgrowth of COCOT service has been the private operation of institutional telephone services. However, “privatization” of phone systems has created a number of technical challenges. Examples of challenges include automated detection of a called party's response to some appropriate prompt (such as, a request for acceptance of a collect call) by dialing a pulse-dial telephone and, in the case of prison systems, the prevention of three-way calling.
Coin telephones owned by local telephone companies generally utilize direct current (DC) signals to signal called-party-answer. This information is transmitted between telephone company central offices and then to the originating pay telephone telling it, in effect, to accept payment for the call. This information is not normally communicated to conventional, i.e., regular business and residential, telephones. Under some tariffs, some, but not all, of this information may be available to COCOT equipment.
Collect calls placed through COCOT equipment are typically handled by an automated operator service (AOS), thus providing the owner of the COCOT equipment with the ability to provide collect call service and bill users of that service for both intra- and inter-local access and transport area (LATA) calls. However, the use of an AOS for collect calls is expensive. In addition, in certain instances, there remains a possibility of fraudulent activity.
In many institutions the phone calls placed by a patient/client or prison inmate are primarily, if not exclusively, collect calls. Collect calls initiated by a patient/client must be indicated as such to the called party. In addition, calls placed by an inmate to an outside party often begin with a prerecorded message stating that the call or collect call is from “a prison” and is being placed by “prisoner's name.” In the above cases the called party is usually asked to dial a digit, commonly a “0” or a “1”, to accept the call or the attendant charges. The phone system providing such service must be able to detect such acceptance both as a dual-tone-multi-frequency (DTMF) tone response from a “touch-tone” phone as well as to detect the equivalent response on a pulse-dial telephone.
The clients/inmates in some institutions may be allowed to call only numbers on a pre-authorized list in order to deter fraudulent activity. Thus, a prison phone system, for example, must be able to detect the called party's flashing the hook switch in order to prevent the called party from activating three-way (i.e., conference) calling, dialing another number and then connecting the prisoner to an unauthorized phone number.
To address the problems described, conventional telephone call handling equipment automatically route local and long distant calls without the intervention of an outside service or live operator. This enables the telephone owner/service provider to charge for the completion of a call or collect call while providing an opportunity to prevent certain calls, e.g., three-way calling. To do this, such conventional systems were configured to detect “hook-flash” conditions, of which several methods of detecting a three-way call initiated by a hook-flash were known in the prior art.
The hook-flash results in a temporary disconnect and reconnect which can be observed as a momentary interruption of loop current at the telephone company central office. The loop current loss, however, is not observed elsewhere in the network nor is the loop current loss made known to the respective parties. Thus, this attribute of a hook-flash is only employed at the central office.
In addition, conventional approaches for detecting initiation of a three-way call have been disclosed in U.S. Pat. No. 5,319,702 (the '702 patent) and U.S. Pat. No. 5,539,812 (the '812 patent). The system disclosed in the '702 patent is based on analog technology and accurately detects a vast majority of attempted three-way calls. The system disclosed in the '812 patent is based on the detection of additional characteristics of the hook-flash signal and utilizes digital signal processing (DSP). The system disclosed in the '812 patent generally is more discerning of the attempted three-way call as well as further equipped to distinguish an attempted three-way call from other events that occur on the telephone line (such as, voice fluctuations, noises from physical contact, e.g. dropping or tapping, of the handset, etc.).
Yet another approach to three-way call detection was disclosed in U.S. Pat. No. 5,768,355 (the '355 patent). The system disclosed in the '355 patent established a baseline ambient, or background, noise level, and detected when the signal noise level dropped below the ambient noise level. When the current signal noise level dropped below the ambient noise level, the system assumed that the called party attempted a three-way conference call.
A problem, however, with this approach is that the ambient noise level during the call may change, which in turn, triggers the particular methodology resulting in a disconnected call. For example, consider an inmate placing a call from a prison phone system. This call is picked up by a person on the receiving end. If that person places the receiver down, e.g., to close a door, there may be a change in the ambient noise level, which results in a disconnected call. The problem is further exacerbated by the fact that re-establishing a call results in another connect charge or may result in the caller, i.e., the inmate, being prohibited from making any further calls for at least a specified period, e.g., one week, based on the phone system configuration and caller profile.
In addition, U.S. Pat. No. 5,504,810 (the '810 patent) discloses a telecommunications network using quasi-time domain reflectometry techniques to identify those telephone calls, which comprise multiple legs. Echo data is collected for the telephone call from a predetermined point in the network to a point where the call originated. The data is processed to generate an indication of whether the telephone call comprises multiple legs, thus identifying those calls most susceptible to unauthorized use. The indication that a telephone call comprises multiple legs is used together with call attribute information, such as whether the call is placed to an international destination, to determine whether a given multiple-leg call is a valid access to the communication system or potentially fraudulent.
However, a problem with this approach is that the '810 patent discloses a method to potentially detect fraudulent access to a telecommunication system. This method can be applied to detect unauthorized access to (ingress) the system from a point other than the point identified as an otherwise legitimate access point. This method provides no means to detect changes in call paths, particularly at the called party end, once the call has been established.
Hence, in view of the above, there is a need for a system and a process to detect and analyze particular signal characteristics that associate with particular activity within an established call in a telephone system so that subsequent analysis on those characteristics allows for evaluating whether an activity beyond the established call has taken place.